$\dfrac{3}{10} - \dfrac{1}{6} = {?}$
Answer: $ = {\dfrac{3 \times 3}{10 \times 3}} - {\dfrac{1 \times 5}{6 \times 5}} $ $ = {\dfrac{9}{30}} - {\dfrac{5}{30}} $ $ = \dfrac{{9} - {5}}{30} $ $ = \dfrac{4}{30}$